Telephone system



June 5, 1945. c. E. LOMAX 2,377,562

TELEPHONE SYSTEM Filed Jul 21, 1944 INVENTOR. CLARENOE- s. LOMAX ATTORNEY Patented June 5, 1945 UNITED STATE TELEPHONE SYSTEM Clarence E. I Jomax, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, a

111., a corporationof Delaware Application July 21, 1944, Serial No. 545,928

19 Claims. (c1. 179-531) a This invention relates in general to telephone systems, but more particularly to small intercommunicating or house systems of the trunk connected type, with secret service; and the primary object of the invention lies in the provision of new and improved circuit arrangements utilizing simple standard mechanisms, which do away with the need for any mechanical locking, in- 'terlocking, or releasingof calling keys.

A particular feature of this invention therefore relates to the improved circuit arrangements whereby standard non-locking push keys or lever keys of a very simple type are used for establishing a call, thuseliminating the need for complicated and delicate locking or interlocking mechanisms for these keys, either with relation to one another, or with relation to the hookswitch or cradle switch of the telephone, such mechanisms being usual with most intercommunicatingsystems.

Another feature of the invention relates'to the circuit arrangements permitting the use of any standard telephone in lieu of some special form of instrument, as is generally required inthis type of system. In the system hereindescribed,

the only external switching function required of the telephone, is to close or open thetwo-conductor line leading from the instrument, when the receiver or handset is removed or replaced, at both calling and called stations. Still another feature of the invention relates to the simple manner in which all selective switching or calling keys are rendered ineffective by removing operating battery therefromwhilea call is in progress, in order to prevent cutting in on an established connection, and therebyto provide secret service.

Another feature is the arrangementwhereby either a calling or called partly can re-ring the j 40 other party by pressing only the ringing key, if said other party should hang up prematurely.

Still'another feature is that whereby a locked outstation, on attempting a call to a busy staindicate that a call is waiting.

A further feature is the provision ofmeans at tion. operates the signal at the wantedstationto j certain special stations permitting such aste tion to cut in on an established connection, or

over-ride the lookout.

An additional feature permits several selective calling keys to be operated momentarily to set up a conference call, whereupon a single operation of the ringing key will simultaneously ring all stations connected to the conference circuit. A party toa conference'call can hang up to leave the conference, and later re-connect by merely againremoving the receiver.

Further features and objects of theinvention' will be apparent from the following description,

reference being made'to the accompanying circuit drawing, in which the extreme simplicity of.

the arrangementis immediately apparent.

With reference to the drawing, which repre-.

sents a schematic or diagrammatic illustration of the invention, equipment and circuits for only three stations A, B, and'C are shown, as being sufficient to permit the invention to be properly described and understood. StationsB and C are represented as being purely local or intercom municating stations, while station A shown at a the upper left, provides for access to a central exchange CX. It will" be understood of course that the number of stations possible in practice,

would be limited chiefly by the traffic requirements, particularly as related to-th'e single intercommunicating trunk.

Each station is provided with a'direct current self-interrupting signal, such as 61, actuated use of a over a separate conductor. This signal may be either a bell or a buzzer, although abell is the Almost any type of standard telephone may be used, sincethe prinpreferred embodiment.

cipal function of this telephone, 'besidespermitting conversation, is to close and open the sub-- scribers line when the receiver or handset is removed or replaced. A ringer is not required; but

' if furnished, will have no effect ontheoperation.

Each station is also provided with an individual select key or call key S l, S2, etc., for each station inthesystem, and a single ringing or signalling key R. These keys aresimple non-locking push buttons, having only two pairs of make contacts (4 springs) for the select keys, and a single pair of make contacts (2 springs) for the ringing key.

It will be understood however that the invention is not limited to the use of push buttons,

and that any other form of non-locking key could be used, without departing from the spirit of the invention, which lies primarly in the circuit arrangement. the preferred embodiment, because of cost, small'size and convenience in use.

Station A shows additional equipment inthe form of a single locking key T which permits con meeting the telephone l5 at this station to a central oflice trunk, represented by conductors-40 An alternating current ringer 43 with y and 4 I. a condenser 42' in series, is also shown connected across the incoming end of this trunk, in order Push keys represent merely their low to provide a signalling means for incoming calls from the central exchange CX. This is done because of the fact that the station telephone, even were it equipped with a ringer, is completely disassociated from the central office trunk when engaged on a local call. Station A also shows how the home select key may be arranged'topermit a special station to breakin on an established; connection, shouldiit be desired" to do so. To provide this service, it'is only necessary to wire up the home key SI as indicated by the dotted lines II and I2. Otherwise the' home key if provided would be left unwiredla u as shown by key S2 at station B, and key,,S3 at station C.

In addition to the foregoingstation equipment a small group of relays is also required, including an individual switching relay SWHSWZ fetcnfon each station of the system, plus three commoners.- lays comprising a battery feed relay 1, a ringing relaysflgtand a lockout1 relay:&. Asinglalocal'talkz ing circuit or talking trunlevisialsovprovidedi represented; by conductors 61: and-:62: andathezassaciatedxzbattery feedxrelay 1; access; toi -whichzis; underitliezcpntrolzof the individuah switching'grer layszg. Aicommoncsourcerofzcurrent isremployedg. with the :positivesterminalagroundedzrionbothtalka. ingcand signallingvpurposesst The: system. iandsithez aliparatussemployedz new;

ingsibeenldescribediia detailed?descript-iomoff the;- operation wil-l'znow be given; in orden 'tozprovider incomplete: understanding ofiztheeinvention:

Assumingztherefore; thatitheesubscriberatistas tiOIIEBi desires torconverse Withttthez subscriber; at,

stationrG} saidrsubscriberB willv first removervhisi 35 receiven (or-."handsetd sucheastfii; This willthavef notimmediatez-efiectthowever;except? to closettherhookswitch: contacts326: and; thus bridge-the:v tele phomaaorosssthe two conductor: linez'consistingzrofir conductors "Hand 1 1i leading from;:the;teleplicne2 to make contacts: 12=; andi-i13iioni the:-=associatedt;

swmswitchingerelayzc v Subscriber B rthenr operates: the: Shvselectskew momentarilwfwhereuporributhzzthes SW23 and the; The

SW2 individuals switchingarelavs operate: circuit: for the operation .of: SW3- is.-as followsr positivezbattery-"throughithenormallytclosedibreak': contacts 4'42 ofttheelockoutvrelay- 9, conductorsslli l 4randi23t uppermaker-contacts ZiwftheSBrseIeot;

keygat' stationzB con'dii-ctorr24t conductor 84;;a'nd

neets the linescon'ductors 1-0-Jand H; from-station;

viding,antindicationiof the busytcondl-tionaofi the B; through.- makee-contacts-li: and'.-,13.--of:-SW2. to-. conductors :6 I I and. .62 ct the? commons. talking trunk leadingeto theecommon batteryr'ieedsrelay 1,,whichioperatesJ oven thiss circuit; and provides talkingbattery tor the: rtrunle' through its. own. windings. The. operation attire-SW3. switching. relay-similarly connects-the. line.-conductors.-t 85 and 86 from: station- C to: the-talking trunk throughimakescontacts;81 and.- 88: of. SW3; The operation ot-.. =the.battemieechrelayg 1 alsa 7a If4however-,; p inss hanewcalla closes make contacts 60 which prepare a circuit to the common ringing relay 8 from all of the ringing keys in multiple. Relay 1 also completes a locking circuit for the operated SW2 and SW3 switching relays so that these latter relays will remain operated upon the release of the operated select key. This circuit is from positive battery throughmake contacts 58 of relay 1, conductor 63%" make contacts'68 andiflflliofi'relhyySWZ and SW3 respectively, and thence through the windingsof the two relays in parallel to negative batfi y.

Subscriber B now momentarily operates the ringing key R, which causes the operation of the commom-signallingrelay 8 from positive battery SWSarelaysz conductors: 66 andwB lg andn thence throughtthezsignalsf 61-5 and: 82. ml parallelitoposietiverbatterw Relay 8: a'ISO'RGIOSBSZ am obviou circuitthrough? itsimakenontacts 5.9itoithe common lockout relay-9 whiclralsooperates: 1

The-lockouttrelay r 9,1 upon operating from relay 8,. completesaa looking circuit iorsitselfiasifollowsz positive:batterwthrnugh makee contactsiik of: the. operatedr-battery' feed r-clays 1', conductorfi'l', make 7 contacts:- 5i6 of: relay," a; 'andwthroughrthe- ;W-inding ofiirelay QLtOI negativebatterys, Theeoperationofi theslockout-zrelay, B a-isosopens the normally closed; contacts 44,. thereby removing: positivegbatteryi from; conductors 45::and .l'deflandihence -from,..all-;

of. thBvSBlECtikGYS. The select keys=areytherzefora rendered ineffective as long asv-relay s-sis,operated;i

thereby preventing.- the; cperatiomtof.- more switching, relays. 1. Inathiss manner access torthe commonctalkingtrunk is=denied:to.-the;othensub scribers; andlthaprivacy-of thesestablished com- 2. nection-. .ispreserved-;.. The-calling station. can 1 9:"?

latten. stationflnottanswer' promptlya To-answe1:, the. called:- subscriber atzstation -C merely removessthe: receiver. onhandset of his telephone, andislthereupon.immediately connected .througlrzto the common-talking trunkbyway oft line conductors .85, and-1.85: andrzmake contacts 81. and-.- 88 ofathe r operated SWiL- switchingv relay.

-- No key operation of any-nature is requiredzat the.

called station: on. anyeinteroommunicating call. ,1 i If another subscriber now attempts-totmake a.

call, thenoperationof-rtheselect keyiwillbe without effect, since. thesakey-sare now. dead-or disabled,

due torthezoperation-of. the lockout relay 9 as previously, explained And-.w-hen the ringing key is operated although-the rcommon'signalling -;relay 8 will operate, the. callingstation signal .will noti 'operate,..due.to,its circuit being openatthe con-v tacts of the associatediswitchingrelay ,thusprop commomtalking trunk. tosthei calling subscriber. Nor Wil'hthe" signalatr the: calledsstation; operate;

except where the called stationtis' one ofsthe-sta tionstinvolvedt. in. thealready, establishedzconnection, Inathatt case theasig-nal at; the :called sta tiontwilli'function since; its associated switching,-

relayis operated and:will-==thusigiveinotica 0t thewaitingscalli i v 2,377,562- is 'equipped for cut-in service, its meme" select I key will be wiredsirnilarly to the indicated S'l key at station A. In such a case," after determining the busy condition in the manneroutlinedin the preceding paragraphQthe calling subscriber may if desired, be switched through to the common talking trunk by pressing the said home key momentarily. This willcause the operation of the individual switching relay associated with that station, and thus permit the new calling subscriber to converse with either or both parties to the connection. In the case of station A for in stance, this circuit maybe traced from direct positive battery at the ringing key, conductor I I,

make contacts ll] of the SI select key, conductor I2, conductor I3, conductor 54, and through the winding of the individual home switching relay SWI to negative battery. Relay SWluponop crating, locks over anobvious circuit to the closed contacts 58 of the" already operated battcryfeed relay'l. V

. Upon completion of a call, release of the equipment is obtained simply byboth parties to the connection restoring their receivers, without any restoration of keys, mechanically or otherwise.-

It will also be obviousthat this is a last party release system, since release is predicated on the restorationto normal of the battery feed relay 1 to which the other relays'lock. And relay 1 cannot restore until the 1ast party involved in a connection has restored his receiver sincesaid relay is held operated over the line circuits in parallel; Restoration of thel receiver by the first party or parties to hang up, thus has no efiecton any operated relay. It is for this reason that the remaining party may recall the other party or parties prior to hanging up, if desired, merely by operating his ringingkey alone. He cannot set up a new connection however without first hanging up, because of the disabled select keys. When the last party hangs up, thecircuit to batteryfeed relay 1 is opened and this relay restores, unlocking lockout relay 9 and the operated switching relays, which also restoregand make the common talking trunkavailable for the next call.

Aconference may be called by any subscriber,- merely by removing the receiver in the usual way,

and then momentarily operating the individual select keys of all of the subscribers wantedin the conference, before pressing the ringing key. This willcause the operation of the calling stations switching relay, as wellas the individual switching relays of the various called stations. The

common battery feed relay I operates upon the operation of the first select key, as previously explained, and provides the usuallocking circuit for the various relays as they -operate,through its makecontacts 58. If now the ringing keyis operated by the calling subscriber, the commonringing relay 8 will operate as previously described, and will cause the signals of all ofthe wanted stations to operate simultaneously.

Lockout relay. 9 also operates at this time and locks up as before, inorder to exclude the othersubscribers, and insure the same degree of privacy for a conference connection as for a regular two party connection. As each station answers by removing the receiver in the usual manner, it is immediately connected. to the common talking trunk, as previously described,with relay 1 furnishing talking battery to all stations in multiple.

Ringing may be repeated as often as necessary, and if one of the parties should leave the conference, he can be recalledby any of theremaining parties merely by the operation of the ringing of the conference stations;

The provision ofa lockingTkey at any station,

as shown at station A in the drawing, permits-a subscriber at suchastation to conneothis telephone to a trunk suchas indicated by conductors 40 and M leading to a central exchange CX. This might be any regular type of common battery exchange, automatic or manual, public or private.

' This T key, being of the locking type, may be left normally switched to the central ofiice trunk or to the intercommunicating system circuit,as desired, depending on the traffic needs. To make an intercommunicating call however, th T key should be operated to connect the. telephone instrument to the local circuit as represented by conductors 52 and 53, before any select key is operated. This is necessary in order to provide a circuit for batteryfeed relay 1, whose operation is required as previously explained, at the time the individual switching relays operate, in order to provide the necessary locking circuits,

When the T key is in a position to connect the line from the telephone to the central office trunk, a call to the central ofliceis made by merely removing the receiver and requesting the connection desired when theoperator answers, or by dialing, if the central oflice is an automatic exchange, and if no operator is provided.

- Incoming calls from thecentralexchange will causethe cperationo'f the standard ringer 43 lective switching keys associated-with each of said lines for controlling the operation--ofgsaid relays, means controlled bythe operation of certain of said relays forconnecting both called and calling subscribers lines to the common talking trunk; a signallingkeyassociated with each of said subscribers lines, means responsive to the operation of said signalling key to signal the called line, and means also responsiveto the operation of said signalling key-to prevent other subscribers from completingconnectionwith the common talking trunk;

2. In a telephone system, a plurality of subscib- I ers lines, a talking trunk common to said lines, a group of relays, a plurality of non-locking selective switching keys'associated with each of said lines for controlling the operation of said relays,

means controlled by the operation of certain of said relays for connectingboth called and calling subscribers lines to the common talking trunk; a signalling key associated witheach of said sub scribers lines, means responsive to the operation of said signalling key wherebyboth called and calling lines are signalled simultaneously; and means also responsiveto the operation of said signalling key for preventing other subscribers from completing connection with the common talking trunk while i-t'is engaged.

3. In a telephone system aplurality of subscribers lines each including atelephone, a talkingtrunk commonto said-lines, a group of re= key. This will of courseoperatethsignals at all I lays}; a p-luralltyr ofenon lockingzselective calling.

scribersi lineseachrincludingea telephone :set; a-

ation ofzsaid relays, means controlledlby -thesoper ation ofcertaimoi saidjvrelaysv for connectirlgsbothf called and calling subscribers? lines to saidxcome' mon intercommunicating; trunk; a; signalling; key

Cfl

and.a::signall' associatedxwitlr each -ofsaid' lines;

. means controlled by said signalling .keyr whereby both calling and; called-.- subscribers signalsrare operated: simultaneously; means-False: controlled by said signalling. key to. exclude the. othensubtscribers from the: intercommunicating trunk whilezitis busy, and-means whereby'such ansexcluded: subscriber upon. attempting-a call-,1 ad: vised oiizthebusy conditionzby theiailure of operation= oftsaidi excluded 1callingsubscribers-signal;

8.- Im a telephone system; a:- pluralityoisube scribersf, lines, a common talkingv trunk; agroup oirelays;a -plurality ofnonelockingselective?call talk-ing trunk commonto said-lines, a groupof relays; aplurality=- of; nonelocking selective:- calling;keys associatedwitheachi oilsaid..-line's for con.- trollingv the, operationof: said: relays, mea-ns con. trolledsby theoperation of certain 'oi said relays for establishingaa connectiombetweembothrcalled and calling. subscribers lines; and said. common talking; trunk; a signallingikew associated with each or saidzlines;means-controlled by saidsignallingkey for signal-ling thecalled subscriber, means also. controlled by+ said -signalling.-, key for. exclude inglother subscribers from the. connection; means whereby thelcalled subscriber answers and is con-v nected-tolthe. common talkingtrunk-merely by.- removing, the:telephoneireceiver or. handset of: said telephone: set-,1 means whereby the connece tion is-released .merelyby both-subscribers.replace ingitheirreceivers or handsetsrof their respecti-v telephone-sets. a v 5. In a. telephone: system a lurality of. subscribers lines cachincluding: awtelephone, a talking tr-unkicom-momto said lines; a group of; relays; a plurality of non-locking selective callingkeys associated with each of said-lines forcontrolling the operatlonof. said relaysemeansr controlled by the operation ofecertai-noi said-relays-for connecting. bothrcal1ed=andccalling; subscribers lines to the-common talking; trunk; means I for signalling the called subscribenand at thezsametime locking ouththel other subscribers: fromthecommon trunk until the; connection} is-released means whereby the-.connectionis released-by bothlsubseribers restoring -.their"receivers;iandtmeansiwhereby either subscribermay recallthe other merelyby a momentary actuation-ct the normal l signalling means, should-said other subscriber have restored his-receiver prematurely H 6. In. atelephone system,atpluralityv of; subscribers lines, an intercommunicatingt-trunk common to saidlines, a groupoof relays, a plurality of non-locking,- selective calling, keys associatedwwith each of said lineseforr controllingthe operation ot said, relays,.means controlled by the operation of certain. oflsaidl relays for establishing; a connectionbetween both'called' and-calling, subscribers linesand said common intercom-- municating-trunk; means foreignallingthe called subscriber andtatlthe-sametime excluding other subscribersfrom the said. connectiom and means. wherebyan attempted-call from such an excluded subscriber. tov one-0f. thevpartiesto saidi conn'ection, will-cause. the operation or the calledsubscriberssignal to indicateeawaiting,calla I 7. In a telephone-system, a plurality. of subscribers lines, an intercommunicating trunk common to said lines, agroup-ofrelays; a: plurality or non-locking'selective. calling; keys; associated with eachrof Saiddinesxfor controlling the: opening-keys associated with eachrofisaidllines for'cone trolling; theioperationaof said relays; meanscion-itrolled by the": operation of 1 certain of said 'relays for connecting both called and calling subscribersi lines-tosaid commomta-lking trunk; axsignalling key associated with; each: of! saidlines, .meansarei sponsive' to: the operationof saidfsign'allingl key to signal the. called; subscriber-;.. means: also" re=- sponsive to=the operation .01 said signallinglkey for: excluding; other: subscribers from the: common. talking trunk while it: is engaged; and means whereby one or more special-.stationsmay estab? lish, connection with said trunk even whilezit is engaged, should: they. desire.

9. In a telephone system, a' plurality of=subt:-"

. scribers. lines; a common talking; trunk; :a group remainingsubscribers;v

of relays; a. plurality 'of' non lockingiselective cal'l oi) ing; keys associated with eachzof said-lines for:

controlling. the operation: ofu saidrvrelaysg. means controlled by; the. operation" I of? certain: of. said relays. for: connecting both. calledpa-ndicalling sub-- I lin'gQkey. for signalling the called subscriber;

means also :responsiveto the soperation ofisa-id key forexcluding other subscribers from the-common trunk while it is :busy; and means :whereby one or morespecial stations may: establish-r connection with the common trunk evenawhile. it is busy; i

whilemaintainingzthe :exclusiontherefrom-10f the 10; Ina telephone systerma plurality-of sube scribersi lines; a common talking-trunk, agroupof relays, a plurality of? non-locking.selective"ca1l+ ing keys: associated with each *ofsaid lines-:tocom trol the operationof'certain of said:relays; a" sige nalling; key associated 'with each of 'said sub'- scribers, lines; means: responsive tov thevoperation' of certain of. said selective -keysf or operating certain of I said relays for connecting several: of: said lines to. the-commonvtrunki atone timein aconferenceconnection, meansaresponsive tOI=thei0perI--l ationv of said signalling} key for signalling: all-30f such connectedlinessimultaneously, and means also responsive to the operatiomof said signalling key forexcludinggathe other subscribers fromzs'aid conferenceconnection.

l1. Inateleph'one system .'a"plurality of sub scribers linesaa common talking-trunk; a groupl of relays, a: plurality of' non -locking selective" calling. keys: associated: with each of said lines" tOvC'OI'ItIQI-the operation of certain: of "said'relays; a signalling. key associated with each of saidlines, means responsive: to? the operation ofcertain ofi said selective: keys. for operating cen tai-n of. saidrelays for connecting three or more at said; lines .to the common trunkt at -one tlme:

rality of subscribers lines,

ling all of such connected lines simultaneously,

and meansrto permit each called conferee to answer and be connected to the common trunk merely by .liftinghis receiver and whereby any confereel can. leave and merelyby restoring and later again removing his receiver. l

.12. In a telephone system, a plurality of subscribers lines, a common talking trunk, a group of relays, a plurality of non-locking selective calling keys associated with each of said lines to control .theoperationof certain of said relays; a signalling key associated'with each of said lines, means responsive to the operation of certain of said selective keys for operating certain of said relays for connecting several of said lines to the common trunk at one time in a conference con nection, means responsive to the operation of said signallingkey at the calling line forsignalling all of such connectedlines simultaneously, means whereby each called conferee joins the conference'by merely removing his receiver and whereby any conferee leaves the conference by merely restoring hisreceiver, and meanswhereby any-of the remaining conferees may recall such absent conferee by a momentary operare-J'oin the conference tion of said remaining conferees signalling key.

l3. In a secret service telephonesystem, a pluan intercommunicatto said lines, a group of renon-locking selective calling ing trunk common lays, a plurality of keys for controlling the operation of said relays,

means controlled by the operation of" certain of said relays for connecting both called and calling subscribers lines to the common intercommunicating trunk; a signalling key associated with each of said subscribers lines, means responsiveto the operation of said signalling key to signalthe called line, means whereby a called subscriber answers and is connected to the intercommunicating trunk merely by removing his receiver, and means associated with one or more of said subscribers lines for answering calls from a central exchange. i i 1 14. In a secret service telephone system, a

plurality of subscribers lines, an intercommunicating trun'kcommon tosaid lines, a group ofrelays, aplurality of non-locking selective calling keys for controlling the operation of. said -relays, means controlled by the operation of certain of said relays for connecting both called and calling subscribers lines to the common intercommunicating trunk; a signalling key associated with each ofsaid subscribersv lines, means responsive tothe operation of said signalling key to signal the called line, means whereby a called subscriber answers and is connected to the intercommunicatingtrunk merely byremoving his receiver, an'd'spe'cial switching and signalling meansassociated with one or more of said subscribers lines for making calls to and receiving calls from a central exchange. l

1,5. In atelephone system, a plurality of subscribers lines and stations, a talking trunk common to said lines, a relay individual to each of said. lines, a non-locking calling key for each of said lines at each of said stations, means respone sive to the operation by a calling subscriber-of the calling key corresponding to the called subscribers line for operating the individual relays corresponding to both calling and called subscribers lines, circuits completed responsive to the operation of said relays for connecting both pleted in "response to the operation by ating the signal device at the called subscriber's station, and means responsive: to the operation of said signalling key. for preventing other subscribers from completing connection with. thecommon talking trunk w le it is engaged. 16. In a telephone system, a plurality of subscribersf lines and stations,=atalking trunk com- .montosaid lines,"a relay individual to each. of said lines, a selecting key corresponding to each of said linesat each of said stations, anindividualconductor .for each of saidrelays, each individual conductor being multipled to allxof'the utilizediselec-ting keys at the corresponding subscribers-station and to the selecting keys corresponding to said ,1 corresponding subscribers station at the other. stations, an operate tor common to saidiselectingnkeys, circuits including said common operate conductor. coma calling subscriber of theiselectingkey at his station corresponding to the called line for operating both the calling and called line individual relays over their said individual conductors and multiple connections, contacts on c said operated calling and called line individual relays for connecting bothjcalling and. called subscribers lineslto the common talking trunk, a battery feed relay connected'to said common talking trunk opresponse to the operation of the signal key at the calling. subscribers station; an individual signal device at each subscribers station, circuits including contacts on the opera'tedindividual relays completed-by the operation of said common signal relay for operating the signal devices at both calling and called stations, alockout relaycommon to said subscribers lines and stations operated in response to the operation of said common signalrelay, a locking circuit for.

said common lock-out relay controlled by said common battery" feed relay, and contacts controlled by the operation of saidlock-out relay for rendering the common operate conductor to the selective keysinefiective to complete operating circuits to any additionalindividual relays, in caseany additional selecting keys are operated while the common talking trunk is thus engaged. l l i 17. In atelephone system, alplurality of sub scribers lines and stations, atalking trunk common to said lines, a relay individual to each of said lines, aselecting key co'rrespondingto each of saidlines at each of said stations, circuits ,in-

cluding an operate conductor common to all of said keys completed in response to the operation by a calling subscriber of the selecting key at his station corresponding tothe called line for operating both the calling and called line individual relays, .contacts on said operated calling and called line individual relays for connecting both calling and called subscribers lines to said common talking trunk, a battery feed relay con the calling and .calledlines to the common talkconducnected-tosaid common talking trunk. operated-in l'responseito the 'connection of said calling-csub- -scriber s dine-to said trunk, :contacts operated by said battery feed relay for locking eachoperate'd individual :relay tin: operated positionl independaently rof thel selective keys; "a signal relay :com-

mon 'to said subscribers lines-and stations, a signalikeyat eac'h-Sstation, :a circuit :includingwther contacts on thebatterytfeed jrelay -:fo-r operating said common-signal relay'insiresponse to the operationsiof the-signal key. at,the:ca1ling*subscribers statioman individualssignal device at each subcontactszcontrolledxby'the:operationof said lock- 1,

outmelayzfor.renderingzthercommon operate conductor to: the selectiveikeysineflective .tocomplete operating circuits ito:;any :-additional- .individual relays, in :case. :anyn-additional sselecting ,@-keys .are

operated: while the rcommon talking trunk. is en-,

. 18; In a telephone :system, la. plurality. of :subscribers lines to .each .of ;saidylines, "a selecting key correspondi-ngvto each :of said; lines-at 24831011 of said stations,

1 a conductor :individual to :eachmf saidindividual relays, connected to allaoirthexsaid selectinglkeys at :the corresponding :suloscribers gstationiand .to each :of said. ..keys corresponding; toysuch -sub-. scribers j line at each. of i the other stations, 0011-. t acts ion each-"of; said 'ndividual relayscomprising signalling contactsclocking contacts, and a pair ofrline'connecting contacts terminating the :corresponding subscrihersline, a :common signalling conductor) connected to-:al1 ofisaid signalling lcontacts,' a :common locking conductor L connected .to all :of said docking pontactava r-com mon talking circuit comprising atpairiofrcommon talkingwconductorsconnected :tto ieachsaid ;pair of line connectingicontacts,latoommon; source f current, -a commonaoperate con uctor normally connected .to-asaid source; andialso:connectedltoteach oi, said selecting :keys forvpperating the;,individual,relays associated .withzbpth calling and calledlines over their individualyconductors infresponse ,to the operation :by gazcalling subscriber ofthe selecting i may -:corresponding to the;-called.;line, thereby to connect both calling-and calledsubscribers lines totthe commomtalking circuit; a common battery ieedtrelayconnected to saidpair of common talking conductors operated over the calling subscriber s ,line ;and;the :line connecting contacts of the corresponding;individualrelay in response to the operation of vsuch {individual -.relay, contacts operated by said battery feed relay for connect ing the common source of current to the common locking conductor to lock theioperated individual relays through :their said locking contacts, signallingmeans individual to; each :subscriberlssta tion connected. to the signalling contacts of the corresponding individual relay, a signal key at and .s'tations,,.:a relay individual each isulos'cribers station,- a common signal .cir-

cuit connected-toeach'oftsaidsignal keys, a;cornmon'signal relay, othercontactsoperatedbysmd lmatteryv feed relay for connecting ,said common apnoea signal :circuit to said signal :relay'sandjforqopere ating said signal relay in response :to the opera.- tiono'f anysignal key, contacts operatediby said signal .relay for operating certain-of esaid: individual signalingxmeansover a :circuit including said common signallingconductor :and tthersi .nalling contacts of the operated ones :of ssaid rindividual relays, and'means' responsive to the roperation of said signal relay for removing-.rsaid commonsource of CllIIBIltf-lOIl'lithe commonopcrate conductor connectedto the selectwekeyszto prevent the operation "of any iadditionalvindiyid- ,ual :relays in case any additional iselectingikeys are'operatedwhile the common talkingscircuit:is engaged. n, 19. In a ,telephone'system, a,plurality:;.of'= subscribers lines and stations, a relayindividua'l {to reach of :said lines, a select key corresponding to each of said lines at eachof:, saidgstationsvcontactsion each :of said individual relays comprising signalling contacts, ,atpair of. line connecting lcontacts terminating the acorresponding subscribers line ga-acommon signalling conductor connected to, all of ,saidgsignalling contacts, a, common locking ;,conductor connected to all of said locking contacts, -.a pair ;of 300111111011 talking said vpair of line connecting contacts, a-- common source of current, a common operate conductor normally connected.to said-sourcaand'zalso connested to each of saidselect ,keysfor-i-operating the individual relays associated-with bothgcalling and called subscribers lines 'in response .to 12116 operation hy a calling subscriber soft .theasel'ect keycorresponding to the i called line, :intorder to connect both :calling and; called subscribers-lines n -.-way; of said pairs of line'connecting contacts to; said common talking conductors, a ;common battery feed relay connectedsto said, pairrof commontalking conductors operated over thecalling subscribers line and the line connecting contacts of the corresponding individual i-relay :in -response;.to the operation of. such, individual rrelay, contacts operated -by.-said battery, feed relay ,forconnecting the 1 common source of current to the common looking conductor tolock'theroper- .atedlindividual relays through their said .locking contacts, signalling means at I each subscriberis station connected to the signalling zcontacts h of r prevent theoperation of -any additional .individual relays incase any additional ,se'lect keyssare operated While the common talking] conductors are thus engaged.

cL aENoE'nroMAx,

locking contacts, and,

conductorsiconnected to-each :for connecting said common 

